Stuck on p.207 of Tom Wolsky's FCE4 book

I'm coming right along on Tom Wolsky's FCE4 book but I'm completely stuck on page 207. Tom says to type "300" in control tab of the Viewer. In the area called "Text Entry and Style" : if I click there to enter anything it will only move the playhead. Where must I enter the "300" (or anything else?). Please advise.